The present invention relates to golf balls and, in particular, to golf balls having at least one layer comprising at least one olefinic polymer produced using a single-site metallocene catalyst in the polymerization process, to which at least one pendant functional group has been grafted by a post-polymerization reaction. The grafted metallocene-catalyzed polymer may be mixed with at least one of an ionomer, a non-grafted or unfunctionalized metallocene-catalyzed polymer, or other non-ionomeric polymer to form a blend, and may be foamed or unfoamed. The layer may be located in any of the cover or core of the ball or in a mantle layer located between the cover and the core.
Three-piece, wound golf balls with balata covers are preferred by most expert golfers. These balls provide a combination of distance, high spin rate, and control that is not available with other types of golf balls. However, balata is easily damaged in normal play, and, thus, lacks the durability required by the average golfer.
In contrast, amateur golfers typically prefer a solid, two-piece ball with an ionomer cover, which provides a combination of distance and durability. Because of the hard ionomer cover, these balls are almost impossible to cut, but also have a very hard xe2x80x9cfeelxe2x80x9d, which many golfers find unacceptable, and a lower spin rate, making these balls more difficult to draw or fade. The differences in the spin rate can be attributed to the differences in the composition and construction of both the cover and the core.
Many attempts have been made to produce a golf ball with the control and feel of a wound balata ball and the durability of a solid, two-piece ball, but none have succeeded totally. For example, U.S. Pat. No. 4,274,637 discloses two- and three-piece golf balls having covers completely or partially formed from a cellular polymeric material to improve backspin, but does not provide any examples that compare the spin rates of the disclosed golf balls with those of prior art balls.
U.S. Pat. No. 5,002,281 et al. discloses a three-piece solid golf ball having an ionomer cover and a solid core consisting of a soft inner core and a hard outer shell, where the difference in the hardness of the two parts of the core is at least 10 on the JIS-C scale.
Similarly, U.S. Pat. No. 4,781,383 discloses a solid, three-piece golf ball, having an ionomer cover and a core with inner and outer layers, where the inner layer has a diameter of 24 to 29 mm and a Shore D hardness of 15 to 30, and the outer layer has a diameter of 36 to 41 and a Shore D hardness of 55 to 65. The percentage of the ball surface which contacts the club face when the ball is struck is 27 to 35%
European Patent Application 0 633 043 discloses a solid, three-piece golf ball with an ionomer or balata cover, a center core, and an intermediate layer. The center core has a diameter of at least 29 mm and a specific gravity of less than 1.4. The intermediate layer has a thickness of at least 1 mm, a specific gravity of less than 1.2, and a hardness of at least 85 on the JIS-C scale.
U.S. Pat. No. 5,703,166 employs compressible materials, i.e., gases, in the core of a solid construction golf ball to simulate the effects of trapped air in a wound ball.
None of these disclosures utilizes the unique physical properties of metallocene-catalyzed polymers, i.e., polymers produced using single-site metallocene catalysts, which produce polymers with a narrow molecular weight distribution and uniform molecular architecture, so that the order and orientation of the monomers in the polymer, and the amount and type of branching is essentially the same in each polymer chain.
The narrow molecular weight distribution and uniform molecular architecture provides metallocene-catalyzed polymers with properties that are not available with conventional polymers, and allow polymers to be produced having unique properties that are specifically tailored to a particular application. The desired molecular weight distribution and the molecular architecture are obtained by the selection of the appropriate metallocene catalyst and polymerization conditions.
Processes for grafting monomers onto polymers and, in particular, polyolefins, are known. European Patent Application No. 0 266 994 discloses a process for grafting ethylenically unsaturated monomers, such as unsaturated carboxylic acids and anhydrides and derivatives thereof, onto copolymers of ethylene. The disclosed process comprises the steps of forming an admixture of the copolymer, monomer, and 25 to 3,000 ppm of an organic peroxide having a half-life of about one minute to about 120 minutes at 150xc2x0 C., and mixing the resultant admixture in an extruder at a temperature above the melting point of the copolymer for a period of time at least four times the half-life of the organic peroxide. The resultant grafted copolymer is then extruded into a shaped article.
U.S. Pat. No. 5,106,916 discloses a process for the catalytic grafting of an ethylenically unsaturated monomer onto a copolymer in which the process of EPA 0 266 994 is modified by the addition of a catalyst comprising water and at least one phosphorous-containing compound selected from the group consisting of compounds of formula HPO(OR1)2, phosphite compounds of formula P(OR2)3 and formula (OR3)Pxe2x80x94Oxe2x80x94R4xe2x80x94Oxe2x80x94P(OR5)2, and di-substituted pentaerythritol diphosphites of formula (R6O)Pxe2x80x94O2xe2x80x94RPEO2xe2x80x94P(OR7), where O2RPEO2 is the pentaerythritol moiety, and R1-R7 are specified organic functional groups.
Grafted metallocene-catalyzed polymers, which are available commercially, share the advantages of non-grafted metallocene-catalyzed polymers, including a narrow molecular weight distribution and uniform molecular architecture. The addition of functional groups to the metallocene-catalyzed polymers by grafting allows polymers to be produced having properties that are not available with unfunctionalized metallocene-catalyzed polymers or polymers formed without the use of metallocene catalysts.
While different blend combinations of species of one variety of polymer, such as ionomers, have been successfully used in the prior art, different polymers, such as ionomers and balata or other non-ionic polymers have not been successfully blended for use in golf ball covers. In general, prior art blends of polymer components are immiscible, i.e., heterogeneous on a microscopic scale, and incompatible, i.e., heterogeneous on a macroscopic scale, unless strong interactions are present between the polymer components in the mixture, such as those observed between ionomers and polymers containing carboxylic acid groups. In particular, this lack of compatibility exists when an ionomer is blended with a polyolefin homopolymer, copolymer, or terpolymer that does not contain ionic, acidic, basic, or other polar pendant groups, and is not produced with a metallocene catalyst. These mixtures often have poor tensile strength, impact strength, and the like. Hence, the golf balls produced from these incompatible mixtures will have inferior golf ball properties such as poor durability, cut resistance, and so on. In contrast, a compatible blend may be heterogeneous on a microscopic scale, but is homogeneous on a macroscopic scale, and, thus, has useful golf ball properties.
In this regard, U.S. Pat. No. 5,397,840 discloses golf ball covers including a blend of xe2x80x9cionic copolymersxe2x80x9d and xe2x80x9cnon-ionic copolymersxe2x80x9d. However, the xe2x80x9cionic copolymersxe2x80x9d are defined as copolymers of an xcex1-olefin and a metal salt of an xcex1,xcex2-unsaturated carboxylic acid, and the xe2x80x9cnon-ionic copolymersxe2x80x9d are copolymers or terpolymers containing ethylene or propylene and acrylic or methacrylic acid monomers. Therefore, strong interactions exist between the metal salts of the xe2x80x9cionic copolymersxe2x80x9d and the acrylic or methacrylic acid monomers of the xe2x80x9cnon-ionic copolymersxe2x80x9d that allow compatible blends to be formed. These interactions do not exist in prior art blends of ionomers and polymers that are truly non-ionic or nonpolar, in particular, those polymers produced with a process that does not involve the use of a metallocene catalyst.
U.S. Pat. Nos. 4,986,545; 5,098,105; 5,187,013; 5,330,837; and 5,338,610 disclose golf balls having covers comprising blends of ionomers and modified thermoplastic elastomers, where the thermoplastic elastomers are conventional polymers, i.e., polymers polymerized using catalysts other than metallocene catalysts. The modified polymers include maleic anhydride modified ethylene-propylene copolymers, maleic anhydride modified styrenic block copolymers, maleic anhydride modified ethylene-vinyl acetate copolymers, brominated styrene-isobutylene copolymers, amine modified ethylene-propylene rubber, and polar modified para-methylstyrene-isobutylene copolymers. However, blends of ionomers with modified polyolefins are not exemplified. Although the disclosed balls are said to exhibit enhanced playability, i.e., softness and spin, without sacrificing coefficient of restitution and, thus, carrying distance, all of the exemplified balls have a Riehle Compression in the range of 61 to 43. Therefore, even though the disclosed cover materials may be relatively soft, each of the disclosed balls has an extremely high compression, and, thus, would be expected to have a high coefficient of restitution.
U.S. Pat. Nos. 5,397,840 and 5,516,847 are directed to golf ball covers comprising a blend of copolymers wherein one or more of the copolymers is a nonionic copolymer, such as a copolymer of ethylene and acrylic acid or methacrylic acid or a copolymer of propylene and acrylic acid, and one or more of the copolymers is an ionic copolymer, such as sodium and zinc neutralized copolymers of ethylene and acrylic acid.
U.S. Pat. Nos. 5,542,677 and 5,591,803 are directed to golfball cover compositions containing blends of high or low carboxylic acid based copolymers and ethylene copolymers such as ethylene alkyl acrylates.
U.S. Pat. No. 5,321,089 is directed to a golf ball cover composition comprising a blend of ethylene-methyl acrylate, an ionomer resin, and a compatibilizer.
As shown in U.S. Pat. No. 5,703,166, metallocene-catalyzed polymers and ionomers form compatible blends of useful golf ball properties. However, there is no known prior art disclosure of golf balls incorporating compositions comprising grafted metallocene-catalyzed polymers.
U.S. Pat. No. 5,981,658 discloses golfball compositions that contain non-ionic olefinic copolymers produced by metallocene catalysts functionalized with a post-polymerization reaction. The disclosed compositions exhibit improved mechanical properties, such as tensile strength and flexural modulus. The polymers disclosed in the ""658 patent do not, however, address problems with processability of these types of polymers.
There is, however, a need in the golf ball art for a golf ball incorporating grafted metallocene-catalyzed polymers and blends of grafted metallocene-catalyzed polymers and other polymers, such as ionomers and non-ionomers, in golf balls, such that the processability of the polymer composition is enhanced because of the resultant increase in melt flow index. Further, the inclusion of foamed and unfoamed grafted metallocene-catalyzed polymers and grafted metallocene-catalyzed polymer blends with certain ionomers and non-ionomers will allow highly durable golf balls to be produced with improved performance and virtually any combination of feel and spin rate.
The present invention is directed to A golf ball comprising a core and a cover, wherein at least one of the cover or the core is formed from a polymer blend comprising at least one grafted metallocene-catalyzed polymer, at least one ionomer, and at least one non-ionomer.
In one embodiment, the golf ball comprises a cover having at least one of a dimple coverage of greater than about 60 percent, a hardness from about 35 to 80 Shore D, or a flexural modulus of greater than about 500 psi, and wherein the golf ball has at least one of a compression from about 50 to 120 or a coefficient of restitution of greater than about 0.7.
In a preferred embodiment, the grafted metallocene-catalyzed polymer has a flexural modulus of from about 500 psi to about 100,000 psi, the ionomer has a flexural modulus of from about 1,000 psi to about 200,000 psi, and the non-ionomer has a flexural modulus of from about 500 psi to about 100,000 psi. In one embodiment, the cover comprises the polymer blend. In another embodiment, the cover layer has a Shore D hardness of less than about 75. In another embodiment, the cover layer has a thickness of from about 0.015 to about 0.125 in. Instill another embodiment, the grafted metallocene-catalyzed polymer has been functionalized by grafting an ethylenically-unsaturated monomer onto the at least one metallocene-catalyzed polymer using a post-polymerization reaction. Preferably, the ethylenically-unsaturated monomer is an olefinic monomer having a functional group selected from the group consisting of sulfonic acid, sulfonic acid derivatives, chlorosulfonic acid, vinyl ethers, vinyl esters, primary amines, secondary amines, tertiary amines, mono-carboxylic acids, dicarboxylic acids, partially or fully ester derivatized mono-carboxylic acids, partially or fully ester derivatized dicarboxylic acids, anhydrides of dicarboxylic acids, cyclic imides of dicarboxylic acids, and ionomeric derivatives thereof, and combinations thereof. More preferably, the ethylenically-unsaturated monomer comprises maleic anhydride.
In another embodiment, the at least one grafted metallocene-catalyzed polymer is present in an amount of from about 5 to about 50 phr. Preferably, the at least one grafted metallocene-catalyzed polymer is present in an amount of from about 5 to about 30 phr. In still another embodiment, the at least one ionomer is present in an amount of from about 95 to about 50 phr. In a preferred embodiment, the at least one ionomer is present in an amount of from about 95 to about 70 phr. In an alternative embodiment, the at least one non-ionomer is present in an amount of from about 1 to about 25 phr. Preferably, the at least one non-ionomer is present in an amount of from about 5 to about 20 phr.
In one embodiment, the core comprises the polymer blend of the present invention. In an alternative embodiment, the core comprises a center and at least one mantle layer disposed between the center and the cover. The at least one mantle layer may comprise the polymer blend while the cover comprises a thermoset or thermoplastic material. Additionally, the cover may comprise the polymer blend and a thermoplastic material. The thermoplastic material may comprise at least one ionomer. Preferred thermoset materials, if used, include polyureas, polyurethanes, and mixtures thereof.
In yet another embodiment, at least one of the core, cover, or mantle layer comprises a density-adjusting filler. The density-adjusting filler preferably comprises zinc oxide, barium sulfate, silica, calcium carbonate, zinc carbonate, tungsten, titanium, and mixtures thereof. In another embodiment, the at least one mantle layer comprises the polymer blend of the present invention. In one embodiment, the center is fluid-filled and, alternatively, in another embodiment, the center is a solid or hollow center. In still another embodiment, the at least one mantle layer comprises a tensioned elastomeric thread disposed about a fluid-filled center or a solid center.
In one embodiment, the grafted metallocene-catalyzed polymer is formed by grafting an ethylenically-unsaturated monomer onto a metallocene-catalyzed polymer selected from the group consisting of polyethylene and copolymers of ethylene with propylene, butene, pentene, hexene, heptene, octene, and norbornene. In another embodiment, the grafted metallocene-catalyzed polymer is formed by grafting an ethylenically-unsaturated monomer onto a metallocene-catalyzed polymer selected from the group consisting of polyethylene and copolymers of ethylene with butene. In a preferred embodiment, the grafted metallocene-catalyzed polymer is formed by grafting an ethylenically-unsaturated monomer onto a metallocene-catalyzed polymer of the formula: 
wherein R1 is hydrogen; R2 is hydrogen or lower alkyl selected from the group consisting of CH3, C2H5, C3H7, C4H9, and C5H11; R3 is hydrogen or lower alkyl selected from the group consisting of CH3, C2H5, C3H7, C4H9, and C5H11; R4 is selected from the group consisting of H, CH3, C2H5, C3H7, C4H9, C5H11, C6H13, C7H15, C8H17, C9H19, C10H21, and phenyl, in which from 1 to 5 H and R4 can be replaced by substituents selected from the group consisting of COOH, SO3H, NH2, F, Cl, Br, I, OH, SH, silicone, lower alkyl esters and lower alkyl ethers, with the proviso that R3 and R4 can be combined to form a bicyclic ring; R5 is hydrogen, lower alkyl including C1-C5, carbocyclic, aromatic or heterocyclic; R6 is hydrogen, lower alkyl including C1-C5, carbocyclic, aromatic or heterocyclic; and wherein x ranges from 99 to 50 weight per cent of the polymer, y ranges from 1 to 50 weight per cent of the polymer and z ranges from 0 to 49 weight per cent of the polymer.
In one embodiment, the polymer blend has a foamed structure. In another embodiment, the non-ionomeric polymer has the chemical structure: 
wherein x=50 to 99 weight %; y=1 to 50 weight %; z=0 to 49 weight %; R1=H or CH3; R2=methyl, ethyl, propyl, butyl, pentyl, hexyl, hectyl, octyl, or isobomyl; and n=0 to 12. In yet another embodiment, the non-ionomer comprises an olefinic homopolymer, an olefinic copolymer, an olefinic terpolymer, and mixtures thereof. Preferably, the non-ionomer is an acid-containing ethylene copolymer comprising ethylene/methacrylic acid, ethylene/acrylic acid, and mixtures thereof In another embodiment, the non-ionomer is an acid-containing ethylene terpolymer comprising ethylene/acrylic acid/n- or isobutyl acrylate, ethylene/methacrylic acid/n- or iso-butyl acrylate, ethylene/acrylic acid/methyl acrylate, ethylene/methacrylic acid/methyl acrylate, ethylene/acrylic acid/iso-bomyl acrylate or methacrylate, ethylene/methacrylic acid/isobomyl acrylate or methacrylate, and mixtures thereof It is preferred that the non-ionomer is present in an amount from about 1 phr to about 25 phr of the total polymer. In an alternative embodiment, the polymer blend further comprises a non-grafted metallocene catalyzed copolymer. Preferably, the non-grafted metallocene catalyzed copolymer comprises polyolefin plastomers, polyolefin elastomers, or a mixture thereof.
The present invention is also directed to a golf ball comprising a core having a center, a cover, and at least one mantle layer disposed between the core and the cover, wherein at least one of the cover, the center, and the at least one mantle layer is formed from a polymer blend comprising from about 5 to about 50 phr of at least one grafted metallocene-catalyzed polymer, from about 95 to about 50 phr of at least one ionomer, and from about 1 to about 25 phr of at least one non-ionomer.
The present invention is also directed to a golf ball comprising a core having a center, a cover, and at least one mantle layer disposed between the core and the cover, wherein at least one of the cover, the center, and the at least one mantle layer is formed from a polymer blend comprising from about 5 to about 50 phr of at least one grafted metallocene-catalyzed polymer formed by grafting an ethylenically-unsaturated monomer onto a metallocene-catalyzed polymer selected from the group consisting of polyethylene and copolymers of ethylene and butene; from about 95 to about 50 phr of at least two ionomers, each comprising an ethylene methacrylic/acrylic acid copolymer wherein at least one ionomer is partially neutralized with lithium and at least one ionomer is partially neutralized with sodium; and from about 1 to about 25 phr of at least one non-ionomer of the chemical structure: 
wherein x=50 to 99%; y=1 to 50%; z=0 to 49%; R1=H or CH3; R2=methyl, ethyl, propyl, butyl, pentyl, hexyl, hectyl, octyl, and isobornyl; and n=0 to 12.